This application claims the priority of Korean Patent Application No. 2001-80903, filed Dec. 18, 2001 in the Korean Intellectual Property Office, which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a projection television, and more particularly, to a projection television with improved brightness to realize a high level of brightness while widening horizontal and vertical angles of view.
2. Description of the Related Art
Image display devices, such as projection televisions or video projectors, are image projection systems that generate images by using image generation means, such as small-sized cathode ray tubes (CRT), liquid crystal displays (LCD), and polymer dispersion liquid crystals (PDLC) as image sources. The image projection systems magnify and project the images onto a large screen to display desired images. Due to the advantages of providing large-sized images, the demand for projection televisions and video projectors has been increasing.
An image projection system is classified as either front-type or rear-type, according to the method of magnifying and projecting images onto the screen.
Referring to FIG. 1, a conventional rear-type projection television includes a cabinet 10, a screen 20 installed on the front surface of the cabinet 10 to form images, and an image generation means 11, such as a CRT, which is installed in the cabinet 10, to generate and radiate the images. The rear-type projection television also includes a projection lens unit 13 for magnifying and projecting the images radiated from the image generation means 11, and a mirror 15 for reflecting the images projected from the projection lens unit 13 toward the screen 20. In the projection television, since the images are projected from the rear surface of the screen 20 in the rear-type projection television, viewers watch the images in front of the screen 20.
In general, a plurality of viewers watch the images displayed on the screen of the image projection system from various angles in a horizontal plane. Accordingly, it is preferable that the images are distributed across a wide range of angles in a horizontal plane.
Consequently, the optical characteristics of the screen of a projection television largely determine the image quality. In particular, the optical characteristics of the screen of a projection television are more important for a large projection television such as a high-definition television (HD-TV), which produces high-definition images.
Referring to FIGS. 2 and 3, the screen 20 of the projection television of FIG. 1 includes a Fresnel lens 20a for converting light incident from the projection lens into a parallel beam. Consequently, image signals formed in the image generation means 11 are displayed through an image projection optical path on the screen 20 as an image with uniform brightness over a large angle of view. In addition, a lenticular lens 20c is adjacent to the front surface of the Fresnel lens 20a. The lenticular lens 20c is used as a light spreading means formed by connecting a plurality of convex unit lenses 20b in parallel. The lenticular lens 20c diverges the parallel beam projected from the Fresnel lens 20a. Each connection portion of the unit lenses 20b of the lenticular lens 20c has a ridge portion 20d on which black stripes are processed.
A front protection plate (not shown) is arranged in front of the lenticular lens 20c to protect the Fresnel lens 20a and the lenticular lens 20c from scratching and dust. Also, the front protection plate is used to improve the contrast of the images.
The front protection plate is formed of a transparent material such as acryl so that images formed on the lenticular lens 20c may be viewed from the outside.
In addition, divergent agents (not shown) such as glasses or polymers may be included in the convex shape unit lens 20b to improve vertical and horizontal angles of view of the lenticular lens 20c. 
According to the conventional screen, although the angle of view is increased by the divergent agents, optical transmittance by backward scattering, reflection, or absorption of image light is decreased, thereby lowering brightness.